Multilayered ceramic capacitor

Abstract

The invention relates to a multilayer ceramic capacitor having dielectric layers and internal electrode layers disposed alternately. The dielectric layers include a dielectric ceramic containing barium titanate as a main component, and also calcium, magnesium, vanadium, manganese, and a rare-earth element. Crystals constituting the dielectric ceramic are constituted by grains containing barium titanate as their main component and containing calcium in a concentration of 0.2 atomic % or less or containing the calcium in a concentration of 0.4 atomic % or more. The crystals grains are also distinct in their relative distributions of magnesium and rare-earth elements between the center of the grain and the surface of the grain. Finally, the relative areas of the two kinds of crystals observed in the plane of a polished surface of the dielectric ceramic are described by a ratio b/(a+b), which is 0.5 to 0.8.

1. A multilayer ceramic capacitor comprising dielectric layers and internal electrode layers disposed alternately, the dielectric layers including a dielectric ceramic containing barium titanate as a main component, calcium, magnesium, vanadium, manganese, and any rare-earth element among dysprosium, holmium, erbium, and yttrium, wherein
 crystals constituting the dielectric ceramic include a first crystal group constituted by crystal grains containing the barium titanate as a main component and containing the calcium in a concentration of 0.2 atomic % or less and a second crystal group constituted by crystal grains containing the barium titanate as a main component and containing the calcium in a concentration of 0.4 atomic % or more; 
 ratios (C 2 /C 1 ) of concentrations (C 2 ) of the magnesium and the rare-earth element contained in center portions of the crystal grains constituting the first crystal group to concentrations (C 1 ) of the magnesium and the rare-earth element contained in surface layers of the crystal grains constituting the first crystal group are respectively larger than ratios (C 4 /C 3 ) of concentrations (C 4 ) of the magnesium and the rare-earth element contained in center portions of the crystal grains constituting the second crystal group to concentrations (C 3 ) of the magnesium and the rare-earth element contained in surface layers of the crystal grains constituting the second crystal group; and 
 b/(a+b) is 0.5 to 0.8 where, in a polished surface obtained by polishing a surface of the dielectric ceramic, a represents an area of the crystal grains constituting the first crystal group and b represents an area of the crystal grains constituting the second crystal group. 
 
     
     
       2. The multilayer ceramic capacitor according to  claim 1 , wherein the dielectric ceramic further contains zirconium. 
     
     
       3. The multilayer ceramic capacitor according to  claim 1 , wherein a content of the zirconium is 0.2 to 1 molar part in terms of ZrO2 based on 100 molar parts of a total amount of an oxide of the barium (BaO), an oxide of the calcium (CaO), and an oxide of the titanium (TiO2). 
     
     
       4. The multilayer ceramic capacitor according to  claim 1 , wherein a variation coefficient (x/σ)×100 (%) is 40% or less where x represents a mean diameter of the crystal grains constituting the first crystal group and the second crystal group and σ represents a standard deviation of diameters of the crystal grains. 
     
     
       5. The multilayer ceramic capacitor according to  claim 1 , wherein a mean diameter of the crystal grains constituting the first crystal group is larger than a mean diameter of the crystal grains constituting the second crystal group. 
     
     
       6. The multilayer ceramic capacitor according to  claim 1 , wherein the dielectric ceramic contains 0.5 to 1 mole of the magnesium in terms of MgO, 0.5 to 1 mole of the rare-earth element in terms of RE2O3, 0.1 to 0.3 moles of the manganese in terms of MnO, and 0.1 to 0.4 moles of the vanadium in terms of V2O5, based on 100 moles of titanium constituting the barium titanate; and a mean diameter of the crystal grains constituting the first crystal group is larger than a mean diameter of the crystal grains constituting the second crystal group. 
     
     
       7. The multilayer ceramic capacitor according to  claim 1 , wherein the dielectric ceramic contains 0.5 to 1 mole of the magnesium in terms of MgO, 0.5 to 1 mole of the rare-earth element (RE) in terms of RE2O3, 0.1 to 0.3 moles of the manganese in terms of MnO, and 0.1 to 0.4 moles of the vanadium in terms of V2O5, based on 100 moles of titanium constituting the barium titanate; the dielectric ceramic further contains zirconium; and a content of the zirconium is 0.2 to 1 molar part in terms of ZrO2 based on 100 molar parts of a total amount of an oxide of the barium (BaO), an oxide of the calcium (CaO), and an oxide of the titanium (TiO2). 
     
     
       8. The multilayer ceramic capacitor according to  claim 1 , wherein the dielectric ceramic contains 0.5 to 1 mole of the magnesium in terms of MgO, 0.5 to 1 mole of the rare-earth element (RE) in terms of RE2O3, 0.1 to 0.3 moles of the manganese in terms of MnO, and 0.1 to 0.4 moles of the vanadium in terms of V2O5, based on 100 moles of titanium constituting the barium titanate; and a variation coefficient (x/σ)×100 (%) is 40% or less where x represents a mean diameter of the crystal grains constituting the first crystal group and the second crystal group and σ represents a standard deviation of diameters of the crystal grains.